The present invention relates to a method of floating glass gobs, a method of manufacturing glass gobs, a method of manufacturing molded glass, and the devices employed in these methods.
In recent years, high-precision hot press molding techniques based on forming molds have been successfully developed as methods of manufacturing aspheric glass lenses and the like. The weight of the prepared member (referred to hereinafter as a xe2x80x9cpreformxe2x80x9d) used in molding must be precise down to the milligram, and the presence of flaws such as striae, devitrification, scratches, and bubbles, as well as surface-adhering matter that cannot be washed away, is not permissible.
For example, a method of mass producing such preforms at low cost is described in Japanese Patent Application Publication No. Hei 2-14839. In that method, molten glass flowing out of a pipe is received in a depression in a forming mold. In this process, a gas such as air or an inert gas is injected through fine holes formed in the depression, creating a layer of gas between the molten glass gob and the inner surface of the depression in the forming mold. Until at least a portion of the outer surface of the molten glass gob reaches a temperature below the softening point, the molten glass gob is held within the depression in a state of substantial non-contact with the inner surface of the depression and cooled to manufacture glass gobs. Based on that method, since both the upper and lower surfaces are free surfaces, preforms of good surface quality can be obtained. Further, in that method, since the molten glass is allowed to drip naturally or is cut with a cutting blade to make it drop, a practical level of weight precision can also be achieved.
Japanese Patent Application Publication Nos. Hei 6-122526, Hei 6-144845, and Hei 6-206730 disclose methods in which a receiving mold comprised of a porous material is employed instead of the above-described forming mold with fine holes, molten glass is received with gas being injected through the receiving mold, and molten glass gobs are similarly held within a depression in a non-contact state and cooled to obtain glass gobs. Further, Japanese Patent Application Publication No. Hei 11-116252 discloses a method in which molten glass is received while gas is being injected through a receiving mold of a porous material having a hemispherical depression and the molten glass gob is rotated in a state of non-contact and cooled to obtain glass spheres. Additionally, Japanese Patent Application Publication No. Hei 10-139465 discloses a method in which molten glass is received in a receiving mold made of porous material that has been soaked in water, a liquid organic compound, or the like and the molten glass is floated by means of gas vaporization pressure and cooled to obtain glass gobs.
However, the above-cited prior art has the following drawbacks. In the method described in Japanese Patent Application Publication No. Hei 2-14839, gas is injected through fine holes in a mold with a depression to float molten glass. In this floating method, when the gas flow rate is increased to completely float the molten glass, pits similar to those on an orange-skin form in the molten glass surface. Since this pitting is formed in the glass by the pressure of gas injected through fine holes, it is necessary to decrease the gas flow rate to a degree where surface pits do not form. However, when the gas flow rate is lowered, it becomes impossible to completely prevent temporary contact between the forming mold and the glass, particularly at the initial stage of glass outflow. Accordingly, the depression surface in this method is machined to a mirror finish to prevent scratching of, and adhesion of dirt onto, the glass surface due to temporary contact.
There is also glass from which preforms of good quality cannot be manufactured by the above-described method. For example, when forming glass in which component volatility is high in the flow temperature range, vapor tends to condense and deposit on the forming mold, which is set to a low temperature. Volatile components that have deposited on the mold then re-adhere to the glass surface through contact between mold and glass. Glasses with high component volatility are glasses containing large amounts of components with high vapor pressures at high temperature, examples of which are alkali components such as Na2O, K2O, and Li2O, as well as B2O3; glasses with high liquidus temperatures; glasses with high viscosities at high temperature; and glasses with high outflow temperatures. Since common glasses contain alkali components, problems tend to occur with volatile matter in glasses with a liquidus temperature of 900xc2x0 C. or above.
Further, even if contact with the mold is prevented, the small amount of floating above the mold increases the concentration of volatile components between the mold and the glass, and the volatile components tend to adhere to the glass. Further, when molding glasses that tend to crystallize (devitrify) near the outflow temperature, contact between the mold and the glass immediately after outflow triggers crystallization and the glass surface sometimes crystallizes. As set forth above, the forming of glass with a large amount of volatile matter in the outflow temperature range and glass tending to crystallize requires that there be absolutely no contact between mold and glass.
Further, the forming of glass with a large amount of volatile matter in the outflow temperature range requires that the gas flow rate be increased to lower the concentration of volatile matter in the gap between the mold and the molten glass and to expel volatile matter from the gap.
A more complete floating state can be achieved by employing a receiving mold comprised of a porous member and rendering uniform the flow of gas that is injected as described in Japanese Patent Application Publication No. Hei 6-122526. However, in practice, the following problems result from the porous member. For example, achieving uniform gas injection requires the selection of a porous member of small pore diameter. However, when a porous member with a small pore diameter is employed, an extremely high gas pressure is required to achieve a gas flow rate adequate for floating, which is a drawback in that the device becomes expensive. Further, when a porous member is employed, there is a drawback in that gas permeability differs substantially between individual molds and the gas flow rate must be substantially adjusted for each forming mold. Although there are various differences, there is a distribution in the gas permeability within a single porous member, making it difficult to achieve a stable floating state. The porous material can be a carbon or ceramic porous material, but these tend to present such problems as low material strength, damage to the porous member during mold assembly, falling off of the surface of the porous member during forming due to thermal shock, and adhesion of fragments to the molten glass surface. Porous members comprised of heat-resistant metals have few of the above-stated problems relating to material strength. However, due to the toughness of the material, the surface pores tend to be crushed during mold processing, often making it impossible to uniformly inject gas.
As set forth above, although a porous member is employed to achieve uniform gas for floating, it is difficult to achieve the intended ideal floating state. There is a further drawback in that mistakes such as forgetting to turn on the gas flow in the mold that result in contact between the mold and the glass tend to damage the mold.
There are additional drawbacks in that porous materials are expensive to buy and to process, and when volatile components have adhered to them, regeneration by washing and grinding is not effective.
The method of floating molten glass by means of the gas vaporization pressure of water or the like in a porous material described in Japanese Patent Application Publication No. Hei 10-139465 has the following problems. To prevent the liquid from evaporating before the molten glass is received in the mold, the temperature of the porous mold must be maintained at below the boiling point of the liquid. Thus, the surface temperature of the molten glass tends to drop precipitously, and when molding large glass gobs, the potential for cracking is high.
Further, in methods employing a mold having pores and in methods in which a porous member is employed as the receiving dish, minute holes must be imparted to the receiving dish, the structure is complicated, and manufacturing costs are thus high. There are further drawbacks in that washing is difficult, the holes become clogged with both grime and volatile matter from the glass, the holes tend to crush, and the service life of the mold is short.
Further, there is a drawback in the prior art methods in that since gas is directly injected at high pressure through fine holes present in the inner wall of a depression or through the holes of a porous member, the portion of the glass gob that is directly struck by the gas always tends to be deformed.
There is a further drawback in the prior art methods, in that when molten glass drops of adequate size first enter the depression, a layered airflow develops between the inner walls of the depression and the glass gob and a floating force is achieved; however, until the molten glass drops reach adequate size, the initial floating state is unstable and contact with the depression tends to occur. There is also a problem in that when the glass gobs are quite small relative to the size of the depression, the gas flow escapes around the glass gob to the top and the floating force is not exerted properly. It is thus necessary to design a floating device corresponding in size to that of the glass gobs.
One object of the present invention is to provide a method of floating glass gobs that solves the above-stated problems and is capable of maintaining a state of non-contact between the glass gob and the depression for keeping the glass gob floating, irrespective of the size of the glass gob.
A further object of the present invention is to provide a method of readily manufacturing glass gobs or spherical glass gobs with good surface quality by maintaining a good state of non-contact between the glass gob and the depression for keeping the glass gob floating, irrespective of the size of the glass gob, even from glass containing numerous components that volatize in the outflow temperature range and from glass with a strong tendency to crystallize.
A still further object of the present invention is to provide a method of manufacturing molded glass by manufacturing glass gobs with good surface quality by maintaining a good state of non-contact between the glass gob and the depression for keeping the glass gob floating, irrespective of the size of the glass gob, even from glass containing numerous components that volatize in the outflow temperature range and from glass with a strong tendency to crystallize, and efficiently molding the glass gobs thus manufactured.
The present invention is configured as follows to achieve the above-stated objects:
A method of floating glass gobs by means of a gas flow employing a device comprising a depression for floating and holding a glass gob, characterized in that said gas flow runs along part or all of the inner surface of said depression from the opening side of said depression toward the bottom of said depression (referred to hereinafter as Method 1).
In Method 1, a gas flow is supplied from a gas flow inlet positioned at the opening end of said depression or on the inner wall between said opening end and the bottom. Examples of the glass gobs that are floated are molten glass gobs and softened glass gobs.
The present invention (a further mode) is configured as follows to achieve the above-stated objects:
A method of manufacturing glass gobs employing a device comprising a depression for holding a molten glass gob by floating and cooling said molten glass gob while floating said molten glass gob by means of a gas flow, characterized in that said gas flow runs along part or all of the inner surface of said depression from the opening side of said depression toward the bottom of said depression (referred to hereinafter as Method 2).
In Method 2, the molten gas gob is obtained by making molten glass flow out of a molten glass outflow nozzle, floating it above a depression by means of the gas flow, and forming it. Further, in this manufacturing method, the molten gas flowing out of the molten glass outflow nozzle can be received by a glass receiving member positioned on the outer portion of said depression, the molten glass received on the glass receiving member can be cut off from the outflow nozzle to form a molten glass gob, and the molten glass gob can then be guided into the depression. In this method, the glass receiving member can be positioned adjacent to the opening in the depression on the device having a depression. Further, the cutting of the molten glass from the outflow nozzle can be conducted by moving the glass receiving member downward or by moving the molten glass outflow nozzle upward. Further, in Method 2, the molten glass gob can be rendered spherical while being floated.
The present invention (a further mode) is configured as follows to achieve the above-stated objects:
A method of manufacturing spherical glass gobs employing a device comprising a depression for floating and holding a molten glass gob to float and simultaneously render spherical by a gas flow a glass gob that has been softened, characterized in that said gas flow runs along part or all of the inner surface of said depression from the opening side of said depression toward the bottom of said depression (referred to hereinafter as Method 3).
The present invention (a further mode) is configured as follows to achieve the above-stated objects:
A method of manufacturing molded glass characterized in that a glass gob obtained by above-described Method 2 is press molded with an upper mold and a lower mold having opposing forming surfaces (referred to hereinafter as Method 4).
A glass gob with a viscosity of 102-1010 poise can be press molded by Method 4.
The present invention (a further mode) is configured as follows to achieve the above-stated objects:
A method of manufacturing molded glass characterized in that a glass gob obtained by above-described Method 3 is press molded with an upper mold and a lower mold having opposing forming surfaces (referred to hereinafter as Method 5).
A glass gob with a viscosity of 102-1010 poise can be press molded by Method 5.
The present invention (a further mode) is configured as follows to achieve the above-stated objects:
A method of manufacturing molded glass by press molding softened glass gobs with an upper mold and a lower mold having opposing forming surfaces, characterized by comprising a step of adjusting a glass gob to a temperature suited to press molding while floating said glass gob by means of a gas flow running along part or all of the depression-shaped forming surface of said lower mold from the opening side of said lower mold toward the bottom of said lower mold; and a step of press forming said glass gob (referred to hereinafter as Method 6).
A glass gob with a viscosity of 102-1010 poise can be press molded by Method 6.
Further, the gas flow in above-described methods 2-6 can be supplied by a gas flow inlet positioned at the opening end of said lower mold or on the inner wall between said opening end and the bottom, and the liquidus temperature of said glass comprising said glass gob can be 900xc2x0 C. or greater.
The present invention (a further mode) is configured as follows to achieve the above-stated objects:
A device for floating and manufacturing a glass gob characterized by comprising a depression for floating and holding a glass gob through the action of a gas flow, and a gas flow supply inlet for generating a gas flow for floating a glass gob, running along part or all of the inner surface of said depression from the opening side of said depression to the bottom (referred to hereinafter as Device 1).
In above-described Device 1, the gas flow supply inlet can be positioned on the opening end of said depression or on the inner surface between the opening end and the bottom. Further, the glass gob can be a molten glass gob or softened glass and the inner surface of the depression can be the forming surface of a press forming mold.
Also, a glass gob manufacturing device characterized by comprising a depression for floating and holding a molten glass gob through the action of a gas flow; a gas flow supply inlet for generating a gas flow for floating a glass gob, running along part or all of the inner surface of said depression from the opening side of said depression to the bottom; and a glass receiving member upon which molten glass from a molten glass outflow nozzle is mounted as the molten glass gob, for introducing said molten glass into said depression, positioned adjacent to said opening of said depression (referred to hereinafter as Device 2).
In Device 2, the gas flow supply inlet can be positioned on the opening end of said depression or on the inner surface between the opening end and the bottom. Further, the inner surface of the depression can be the forming surface of a press forming mold.